<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>
<script type="text/javascript">
	
	var a = top;
	var b = parent;
	var c = window;
	var d = this;
	var e = self;

	a.c = 10; //window.c = 10;
	c.c = 20;
	alert(e.c.c)//self == window.c
	//alert(e.c.c);//20 o//undefied
	//alert(c.c);//20 o//undefied



</script>
</body>
</html>